Epidemiology is the basic science and most fundamental practice of public health and preventive medicine. We can study health and disease by observing their effects on individuals, by laboratory investigation of experimental animals, and by measuring their distribution in the population. The epidemiologist uses each of these approached to investigate health and disease in populations. Epidemiology is therefore the scientific foundation for the practice of public health.
The word “epidemiology” comes from epidemic, which translated literally from the Greek means “upon the people.” Historically, the earliest concern of the epidemiologist was to investigate, control, and prevent epidemics. This chapter deals with the scientific principles that are the foundation of epidemiology. It first addresses the sources and characteristics of information used to assess the health of populations. Next, some essential elements of the practice of epidemiology will be discussed, as well as challenges to that practice. Finally, the evolution and newer techniques for epidemiology in controlling and preventing health problems will be presented.
A BRIEF HISTORY OF EPIDEMIOLOGY
Epidemiology has roots in the Bible and in the writings of Hippocrates, as does much of Western medicine. The Aphorisms of Hippocrates (fourth to fifth century BC) contain many generalizations based on prolonged and careful observation of large numbers of cases. The introductory paragraph of Airs, Waters, Places offers timeless advice on good environmental epidemiology:
Whoever would study medicine aright must learn of the following subjects. First he must consider the effect of each season of the year and the differences between them. Secondly he must study the warm and the cold winds, both those that are common to every country and those peculiar to a particular locality. Lastly, the effect of water on the health must not be forgotten. When, therefore, a physician comes to a district previously unknown to him, he should consider both its situation and its aspect to the winds. Similarly, the nature of the water supply must be considered. Then think of the soil, whether it be bare and waterless or thickly covered with vegetation and well-watered, whether in a hollow and stifling, or exposed and cold. Lastly consider the life of the inhabitants themselves, are they heavy drinkers and eaters and consequently unable to stand fatigue or, being fond of work and exercise, eat wisely but drink sparely?1
Epidemics of infection were serious concerns for physicians in ancient times, although often they could do little more than observe the victims and record mortality. Their limited knowledge rarely permitted effective intervention. Until the Renaissance in the fourteenth through sixteenth centuries, physicians based their approach more on impressions than real numbers. John Graunt is often regarded as the founder of vital statistics. He first published his numerical methods for examining health problems in Natural and Political Observations on the Bills of Mortality in 1662. He was the first to attempt this approach.